An example of a countermass and a countermass weapon according to the above is previously known from SE patent 8205956-9 (publication number 444 722). According to said patent the liquid is enclosed in a shell construction in the shape of a plastic container. It is important that such a container cracks in a controlled manner. To this end measures have been done to improve the cracking procedure for instance by introducing fractural impressions. Nevertheless it is a problem that the container may crack in an uncontrolled way mainly due to non-cracking in the intended fragmentations. This may result in that fragments having a high velocity are ejected backwards from of the launcher tube resulting in that the requirements on the back blast area not are fulfilled.